Wikipedia articles cover topics at several levels of detail: the lead contains a quick summary of the topic's most important points, and each major subtopic is detailed in its own section of the article. The length of a given Wikipedia article tends to grow as people add information to it. This does not go on forever: very long articles would cause problems and should be split.

A fuller treatment of any major subtopic should go in a separate article of its own. The original article should contain a section with a summary of the subtopic's article as well as a link to it. For copyright purposes the first edit summary of a subtopic article formed by cutting text out of a main article should link back to the original.

It is advisable to develop new material in a subtopic before summarizing it in the main article. Templates are available to link to subtopics and to tag synchronization problems between a summary and an article it summarizes.

Articles over a certain size may not cover their topic in a way that is easy to find or read. Opinions vary as to what counts as an ideal length; judging the appropriate size depends on the topic and whether it easily lends itself to being split up. Size guidelines apply somewhat less to disambiguation pages and to list articles, especially if splitting them would require breaking up a sortable table.

Longer articles are split into sections, each usually several good-sized paragraphs long. Subsectioning can increase this amount. Ideally many of these sections will eventually provide summaries of separate articles on the subtopics covered in those sections. Each subtopic or child article is a complete encyclopedic article in its own right and contains its own lead section that is quite similar to the summary in its parent article. It also contains a link back to the main parent article and enough information about the broader parent subject to place the subject in context for the reader, even if this produces some duplication between the parent and child articles. A link such as "Main page: Wikipedia:Splitting", generated by the template {{Main|<name of child article>}}, is placed below the section heading of the summary in the main article. Other template links include {{Details}} and {{Broader}}. For article pairs with a less hierarchical parent/child relationship {{See also}} may apply.

Each article on Wikipedia must be able to stand alone as a self-contained unit (exceptions noted herein). The verifiability policy requires that all quotations and any material challenged or likely to be challenged be attributed to a reliable, published source in the form of an inline citation. This applies whether in a parent article or in a summary-style subarticle.

Editors are cautioned not to immediately split articles if the new article would meet neither the general notability criterion nor the specific notability criteria for their topic. Instead, editors are encouraged to work on further developing the main article first, locating coverage that applies to both the main topic and the subtopic. Through this process, it may become evident that subtopics or groups of subtopics can demonstrate their own notability, and thus can be split off into their own article. If a concept can be cleanly trimmed, removed, or merged elsewhere on Wikipedia, these steps should be undertaken first before some new article is created.

If possible, split the content into logically separate articles. If necessary, split the article arbitrarily. Long stand-alone lists may be split alphanumerically or chronologically or in another way that simplifies maintenance without regard to individual notability of the subsections (common selection criteria: lists created explicitly because most or all of the listed items do not warrant independent articles; short, complete lists of every item that is verifiably a member of the group). However, a split by subtopic is preferable. Judging the appropriate size depends on the topic.

Whenever you break up a page, please note the split (including the subtopic page names between double square brackets) in the edit summary. Add {{Main}} to the top of the section in the parent article to indicate where the detailed article for that section is.

In applying summary style to articles, care must be taken to avoid a POV fork (that is, a split that results in the original article or the spinoff violating NPOV policy), a difference in approach between the summary and the spinoff, etc.

Where an article is long, and has lots of subtopics with their own articles, try to balance parts of the main page. Do not put undue weight into one part of an article at the cost of other parts. In shorter articles, if one subtopic has much more text than another subtopic, that may be an indication that that subtopic should have its own page, with only a summary presented on the main page.

Sometimes editors will add details to a summary section without adding those facts to the more detailed article. To keep articles synchronized, editors should first add any new material to the appropriate places in the detailed article, and, if appropriate, summarize the material in the summary section. In other cases, the detailed article may grow considerably in scope, and the summary section will need to be rewritten to do it justice. These problems may be tagged with {{Sync}}.

To eliminate this maintenance burden, editors can use partial transclusion as explained at Wikipedia:Transclusion#Partial transclusion. However, discussions in 2010 highlighted issues with viewing historical renditions of the main page (the partial transclusion will be from the current subpage, which may even have been deleted). Therefore it seems to be recommended to use this process only with consensus and when articles are rapidly evolving.

Article and list topics must be notable, or "worthy of notice". Notability guidelines only outline how suitable a topic is for its own article or list. They do not limit the content of an article or list.

If only a few sentences could be written and supported by sources about the subject, that subject does not qualify for a separate page, but should instead be merged into an article about a larger topic or relevant list. It is not uncommon for editors to suggest that articles nominated for deletion instead be merged to a parent article.

Unless all subarticles of a summary-style article are truly compliant to the common-names principle, it is a good idea to provide a navigational template to connect the subarticles both among themselves and along with the summary-style main article.

Summary style is a good way to give more structure to a long bibliography or list of external links. For example, the World War II summary-style article portrayed above could have a "Further reading" or "External links" section that treats the history of World War II as a whole, while a subarticle on the Pacific War could have "External links" containing works that deal with World War II in the Pacific region.

For planned paper Wikipedia 1.0, one recommendation is that the paper version of articles will be the lead section of the web version. Summary style and news style can help make a concise intro that works as a standalone.

This style of organizing articles is somewhat related to news style except that it focuses on topics instead of articles. The idea is to summarize and distribute information across related articles in a way that can serve readers who want varying amounts of details, thus giving readers the ability to zoom to the level of details they need and not exhausting those who need a primer on a whole topic. Breakout methods should anticipate the various details levels that typical readers will look for.

This is more helpful to the reader than a very long article that just keeps growing, eventually reaching book length. Summary style is accomplished by not overwhelming the reader with too much text up front, by summarizing main points and going into more details on particular points (subtopics) in separate articles. What constitutes "too long" is largely based on the topic, but generally 30 kilobytes of readable prose is the starting point at which articles may be considered too long. Articles that go above this have a burden of proof that extra text is needed to efficiently cover their topics and that the extra reading time is justified.

Sections that are less important for understanding the topic will tend to be lower in the article (this is news style applied to sections). Often this is difficult to do for articles on history or that are otherwise chronologically based, unless there is some type of analysis section. Organizing in this way is important because many readers will not finish reading the article.

Wikipedia is not divided into a macropædia, micropædia, and concise version, as is the Encyclopædia Britannica—we must serve all three user types in the same encyclopedia. Summary style is based on the premise that information about a topic should not all be contained in a single article since different readers have different needs:

many readers need just a quick summary of the topic's most important points (lead section),

others need a moderate amount of information on the topic's more important points (a set of multiparagraph sections), and

some readers need a lot of details on one or more aspects of the topic (links to full-sized separate articles).

The parent article should have general summary information and the more detailed summaries of each subtopic should be in child articles and in articles on specific subjects. This can be thought of as layering inverted pyramids where the reader is first shown the lead section for a topic, and within its article any section may have a {{Main|<subpage name>}} or similar link to a full article on the subtopic summarized in that section (for example, Yosemite National Park#History and History of the Yosemite area are two such related featured articles). The summary in a section at the parent article will often be at least twice as long as the lead section in the child article. The child article in turn can also serve as a parent article for its specific part of the topic, and so on, until a topic is very thoroughly covered. Thus, by navigational choices, several different types of readers each get the amount of details they want.